Gaseous fuel engines are known for their ability to burn clean relative to their compression ignition engine counterparts. However, gaseous fuels are well known for the difficulty in attaining successful ignition. Some gaseous fuel engines utilize a spark plug, whereas other engines are known for utilizing a small amount of distillate diesel fuel that is compression ignited to in turn ignite a larger charge of gaseous fuel. In these engines, the gaseous fuel may be supplied to the engine intake manifold or metered directly into individual cylinders where it is mixed with air prior to being ignited responsive to the pilot diesel injection near top dead center. While this strategy may reduce NOx due to a cooler combustion, hydrocarbon emissions may be relatively high and there is no ability to control combustion characteristics, such as reaction rate, to accommodate different engine operating conditions.
U.S. Pat. No. 7,373,931 teaches a dual fuel engine that utilizes a small quantity of compression ignited distillate diesel fuel to ignite a larger charge of gaseous fuel injected after ignition. This reference teaches the use of a fuel injector with nested needle valve members to facilitate injection of both the gaseous and liquid fuels from the same injector into each engine cylinder. In other words, the patent owner teaches direct injection of gaseous fuel into the engine cylinder after a pilot quantity of diesel fuel has been injected and ignited. While the reference claims that this strategy provides improved efficiencies over the counterpart gaseous fuel engines discussed previously, other emissions problems and power inefficiencies, especially at higher speeds and loads may be present.
The present disclosure is directed toward one or more of the problems set forth above.